ISLAMABAD, Pakistan (CNN) -- A suspected U.S. missile strike killed four people and wounded two others in Pakistan's tumultuous North Waziristan region, Pakistani military sources said Sunday.

The Saturday strike hit a home in the village of Khatai Qila, the sources said, speaking on condition of anonymity because they are not authorized to speak to the media.

The attack was one of two suspected missile strikes on Saturday in the tribal region that borders Afghanistan.

A second strike hit the village of Matches but did not wound anyone, the sources said.

Staffers with the NATO press office and the U.S. military in Afghanistan declined to comment on the strikes. The U.S. Embassy in Islamabad also had no comment.

The United States, which has a presence in Afghanistan, is the only country operating in the region with the known capability to launch missiles from remote-controlled drones.

The U.S. maintains that Taliban and al Qaeda forces operate with relative impunity in tribal areas along Pakistan's mountainous border with Afghanistan. The U.S. accuses extremists of using the area as a staging ground to attack U.S. forces and their allies in Afghanistan.

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There have been several reports recently of suspected U.S. missile attacks on militant targets in Pakistan.

Among the alleged U.S. attacks:

• On Thursday, a suspected missile strike in North Waziristan struck the village of Tapi and killed eight people, military sources said.

• On October 5, rockets landed near the family home of a top politician in northwest Pakistan, The Associated Press reported, quoting officials.

• On October 3, Pakistani intelligence officials told AP, a suspected U.S. strike in North Waziristan may have killed a senior Taliban militant.

• Also on October 3, a suspected missile killed at least 20 people in the Pakistani village of Lund Mohammad Khel in North Waziristan, a military source told CNN.

• On October 1, two or three suspected U.S. missiles struck a home in North Waziristan, Pakistani military sources said.

• And last month, the U.S. military reportedly sent ground forces into South Waziristan -- also a tribal area -- without Islamabad's permission. U.S. and Pakistani troops exchanged fire after Pakistani soldiers fired "anticipatory warning shots" at two U.S. helicopters that Pakistan officials said crossed the border. U.S. military officials said the helicopters were in Afghan territory.

Media reports have said that several months ago, President Bush authorized U.S. special forces to carry out ground assaults inside Pakistan without seeking Islamabad's permission.

U.S. attacks in Pakistan have infuriated Islamabad, which says such raids violate the nation's sovereignty.

President Asif Ali Zardari said last month that Pakistan would not allow foreign forces to enter his nation without permission, even to pursue extremists.

"We will not tolerate the violation of our sovereignty and territorial integrity by any power in the name of combating terrorism," he said in his first speech to Parliament as president.

His remark followed a similar declaration from Pakistan's military chief, Gen. Parvez Kayani, who said that Pakistan's territorial integrity "will be defended at all cost, and no external force is allowed to conduct operations."